I have studied your case.
In fusion surgery result of surgery are good if good union of vertebra occurs post fusion.
Proper rest will give early fusion.
So advise him to rest now.Use lumbar corset for support.
It may take 3 months time for complete rehabilitation
You can consult physiotherapist for help.
I will advise to check your vit B12 and vit D3 level.
Hope this answers your query. If you have additional questions or follow up queries then please do not hesitate in writing to us. I will be happy to answer your queries.
Wishing you good health.